Method of heat treating steel wire and apparatus therefor



Oct. 27, 1942. w. H. WOOD ET AL 2,300,329

METHOD OF HEAT TREATING STEEL WIRE AND APPARATUS THEREFOR Filed Feb. 18, 1938 4 Sheets-Sheet 1 1NVENTOR5 ZJz'l/iam f7. Uooa m/ Oscar C". Fazzfirzm gaym cv Oct. 27, 1942. I w. H; WOOD ETAL 2,300,329

METHOD OF HEAT TREATING STEEL WIRE AND APPARATUS THEREFOR Filed Feb. 18, 1958 4 Sheets-Sheet 2 ATTO Y6 55; v MIL 71km f/ @0062 4114 H 1NVENTOR Oct. 27, 1942. w. H. WOOD ET AL 2,300,329

METHOD OF HEAT TREATING STEEL WIRE AND APPARATUS THEREFOR Filed Feb. 18, 1938 4 Sheets-Sheet s BY 0 C. Tina/m 4% avg :TTO EYS.

--W. H. wooD ETAL Oct. 27, 1942. 2,300,329

METHOD OF HEAT TREATING STEEL WIRE AND APPARATUS THEREFOR Filed Feb. 18, 1938 4 Sheets-Sheet 4 5 4 6 mw m N d R wa wm N040 T 3. z C My mm mm;

Patented Oct. 27, 1942 sr rs r William H. Wood, South Euclid, and Oscar C. Trautman, Parana, Ohio Application February 18, 1938, Serial No. 191,292

9 Claims.

Our invention relates to apparatus for and method of heat treating steel in the form of wire and the like, in continuous operation; In the heat treatment of steel in continuous operation as practiced by the usual methods, the heating is effected by passing the material through a heatin furnace which is preferably gas-fired. Many objectionable features attend this method. The surface of the wire becomes decarburized in spots, the heating is accomplished at a slower rate than is desirable, and it is necessary to heat the material to a, substantially higher temperature than that at which it is desired to quench for hardening. Other have recognized these disadvantages and have sought to heat the material under treatment by its resistance to the passage of an electric current therethrough. For fifty years such attempts have been made, but none of the methods have gone into use, and the devices of these earlier attempts have made no impression on the practices of the industry.

The object of our invention paratus and method whereby in continuous operation steel wire and the like is heated by its electrical resistance to a temperature at which its iron content assumes the gamma form, and is then rapidly partially quenched from its maximum temperature to a desired controlled temperature, from which it may be further treated or allowed to cool to atmospheric temperature.

A further object is to provide apparatus and is to provide apmethod whereby the material thus partially quenched to a controlled medlately in continuous operation further quenched to atmospheric temperature under controlled conditions which impart to the steel the qualities demanded in spring steel.

A further object is to provide apparatus and method whereby the said material, partially quenched to a controlled temperature, is immediately reheated by its electrical resistance and held in a desired temperature range whereby the steel is given the qualities desired in wire which is to be further reduced by drawing.

And a further object is to provide apparatus and method whereby material is heated by its electrical resistance, is partially quenched to a controlled temperature in the molten metal of an advance electrode, and is held at such temperature for a controlled period of time, whereby a heat treatment practically identical with that known as patenting is given the material, but with decidedly marked increase in those qualtemperature is im- March 23, 1937, now Patent ities desired in a Wire which is to be reduced by drawing.

Other objects of our invention will appear from the description hereinafter given and include apparatus and method whereby we can combine in continuous operation with said heating and quenchingsteps such treatments as tempering the spring steel wire, or such as pickling, coating,

etc., of the patented wire in preparation for the draw.

In addition to avoiding the disadvantages of furnace heating hereinabove set forth, we have in our new method distinct advantages which will be readily recognized. The equipment for the practice thereof is cheaper and is not subject to depreciation in use except in the slightest degree. Such equipment is ideally adapted for combination with that which is required to give the heat treated wire further processing in preparation for any particular use. The heating of the wire is so rapid, being at a uniform rate throughout any cross-section, and the wire is at a high temperature so short a time that little or no scale is formed. Such as may be formed we have removed by an 8 to 10 second dip in a. 5% acid solution which was given in continuous operation and followed in continuous operation by a reheating of the wire to about 400 F. by electrical resistance, whereby the occluded hydrogen was driven off. The wire during heating may be easily enclosed for the conservation of heat or for the use of any special atmosphere which may be desired.

This application is a continuation of our c0- pending application Serial No. 132,580, filed December 17, 1940.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means and steps hereinafter fully described and particularly pointed out in the claims; the annexed drawings and the following description setting forth in detail certain means and modes of carrying out the invention, such disclosed means and modes merely illustrating various ways in which the principle of the invention may be used.

It is believed that our explanations of method will be more readily understood if the apparatus which we have invented for the practice of said method is first described. This apparatus is shown diagrammatically in the iirawings, in which Figs. la, 1b, 1c and 1d combined show a. plan view of our apparatus as used to heattreat wire for use in springs; Figs. 2a, 2b, 20

No. 2,224,998, issued low melting point.

and 2d combined show an elevational view of the same in cross-section on line 1-1.

The embodiment of our novel apparatus shown in the drawings has proven highly efficient in operation. It is designed to handle a maximum of six wires at a time. The wires I being treated are each drawn through the apparatus from left to right by constant speed reels of standard type, which reels are not shown. The wires are supplied to the machine from feed reels of the usual type which are not shown, but preferably. will be of capacity such that each will hold a days run of wire in a single continuous strand.

On a suitable frame 2 a contact pot 3 is mounted at a slight elevation. At either end of said pot is positioned a set of sheave wheels 4 mounted on a common bearing shaft 5, said wheels being insulated from each other and from said shaft by spacers 6 and bushings Beneath the set of sheave wheels over which the wires first pass in entering the machine is a pan 8 of oil so positioned that the peripheries of the wheels 4 will touch the oil and, on revolving, will carry it upward and coat the wires passing thereover. Between said set of sheave wheels and the said contact pot a wire wiper 9 of felt is so placed that the said wires are drawn therethrough before they enter said contact pot 3.

The sides, ends and bottom of said contact pot 3 are heat insulated and are of di-electric material. Within said pot 3 are nested long narrow metallic troughs Hi, of which there is one for each wire to be treated, and each of which is substantially filled with a metal or alloy H of These troughs are electrically insulated from each other and each has mounted on one side at the mid-point a wire sinker I2, which is electrically insulated from the supporting side of the trough. These sinkers |2 each comprise a depending arm |3 of fiat heat-resisting material, having a small roller |4 rotatably mounted on one face thereof, so positioned and mounted that it will rotate, below the surface of the molten alloy, and in a plane parallel to that of the flat arm.

In the bottom of each trough I0 is mounted an electric heating element IE to which current is supplied from a source of electricity (not shown) by means of the lead wires l6 mounted through the end wall of the pot 3. Also mounted in each trough I0 is a thermostatic bulb protective tube H, in which a thermostatic bulb is placed which, through the lead I8, mounted through the wall of pot 3, controls the supply of heating current to the lead wires l6 connected with the heating element by devices and connections well understood in the art.

Mounted through the bottom of the pot 3 and in electrical connection with the alloy H in the troughslfl are electrical connector studs IQ, of which there is at least one for each trough ID.

A layer of fine granular carbon over the surface of the alloy protects it from oxidation when molten.

In spaced longitudinal relation with the contact pot 3 is a-quenching pot 2| containing molten metal, but at a lower elevation. Said quenching pot 2| comprises a single container 22 formed of metal which is electrically insulated, and also protected by heavy heat insulation 220.. Copper cooling fins 23, mounted longitudinally on the bottom of the metal container 22 extend into a passage 24 through which cooling air is circulated for the control of temperature in said container 22.

Mounted between the said contact pot 3 and said quenching pot 2| with an end supported by each is a long open ended box 25 formed of dielectric material having a low value as a conductor of heat, which box is divided by partitions into separate closures for the'passage of Said box 25 conserves heat the several wires. but is also most useful when a wire breaks, as it prevents the end of the broken wire from contacting the other wires in the heating zone.

For convenience in varying the length of the heating space between the contact pot 3 and the quench pot 2|, these may preferably be so mounted as to be longitudinally adjustable. When said heating space is shortened, the box 25 will be omitted or a shorter one substituted.

An electrical connector 26 mounted through the wall of the pot 2| makes electrical contact with the metal container 22. A suitable source 21 ofv electric heating current is connected in series between the said connector 26 and the saidstuds IS, in a circuit 28 which is completed through the medium of the molten metal in said pots 3 and 2| and the wires I being heated therebetween.

Other circuits 29 connect the said connector 26 with each of the contact plugs l9 and in each of these circuits is a condenser 30 which provides a by-pass for potentials of E. M. F. which without such path would cause anarc between the molten metal of the bath and the wire drawn therefrom. In the embodiment shown such condensers are of the paper wound type and are of 10 micro-fared capacity. A

In the quench pot 2| is a bath 3| of molten solder. In the embodiment shown we have used eutectic PbSn. This solder is maintained at the desired temperature of quench by electrical heating units 32 submerged therein, which are controlled in a manner well understood in the art and which in combination with the cooling effect of the fins 23, exposed as explained to the air driven through the passage 24, maintain the temperature of the molten solder within a narrow range.

A pair of spaced bars 33 mounted transversely of the quenching pot 2| each support a plurality of sinkers 34, one being provided on each bar for each wire to be treated. These sinkers 34 are similar in construction to the sinkers 2 used in the contact troughs l0. Provision may be made for moving these bars longitudinally of the pot, whereby it is possible to modify the time interval wires will stay in the quench of molten metal when running at a particular speed.

The surface of the molten solder bath 28 is protected from oxidation by a covering of oil which covering is divided into two sections by a dam 35 positioned in the surface of the solder midway the pot 2| and between the two sets of sinkers 34. On the surface of the solder'at that end of the pot 2| in which the wires enter we maintain a thincovering of tempering oil 36, which is supplied by nozzles 31 positioned near the dam 35 and escapes through an outlet 33 in the end wall of the pot 2|. This oil is circulated through tubing and a pump which are not shown but are connected with said outlet 38 and nozzle 31 in a conventional manner. On the other section of the bath surface we maintain a substantial thickness of quenching oil 39 which oil has purposes other than protecting the bath surface and is continuous with the body of oil in an oil quench pan 40 with which it will be next described.

Positioned adjacent the discharge end of said quench pot 2| and in longitudinal relation therewith is an oil quench pan 40 containing a quenching oil 4|. Through the wall of the quench pot 2| at the discharge end above the molten solder are a plurality of apertures 42 affording access to the adjacent pan 40, one being provided for the passage of eachwire I. The quenching oil 4| flows through said apertures 42 onto the surface of the molten solder bath 3| to an overflow trough 43 adjacent the dam 35. Near the apertures 42 and within the quench pot 2| a small roller 44 is so mounted that the Wires passing thereover are guided centrally through the apertures 42. Placed within the quench pan near said apertures 42 is a dam 45 over which the quenching oil 4| news to and through said apertures 42 onto the molten solder bath 3|. The top of said dam 45 has tapered grooves 46 through which the oil 4| flows and which are'so positioned that the wires I pass therethrough as they are drawn from the apertures 42. Similarly the quench oil 4| overflows a second similar dam 41 at the discharge. end ofthe quench pan 40. The oil so overflowing and the oil from the overflow 43 is collected in a reservoir 48 positioned below the pan 40, and after cooling is returned to the pan 40 by the inlet 49 midway of the pan 40. The connections for this circulating, and the cooling and pumping means are conventional and are not 'shown. A valved sump 50, positioned adjacent the quench pot 2|, in the pan 40, permits by-passing oil instead of flowing it through the apertures 42 to'the over-flow trough 43. This valved sump 50 discharges direct to the reservoir 48.

An oil wiper 5| is positioned adjacent the discharge end of the pan 40 and rollers 52 are provided over which the wires are guided into a temper pot 53 as they are drawn from the oil 4| and through the wiper 5|. The temper pot 53 is conventional and is heated by electric heating elements 54in a conventional manner.

It will be understood that standard reels taking up a-constant speed are placed beyond the temper pot 53 which reels draw the several wires I through the several sections of the described apparatus.

The several parts of our apparatus have been described in the relation in which they are used in heat-treating steel wire for springs according to our new method which will now be described.

New method of heat treatment I The essential steps, used in all applications of our method of heat-treating steel in the formof wires and the like, however said method may be modified to secure a particular desired final result, are the following: (1) the wire under treatment is heated by its resistance to the flow therethrough of an electric current supplied thereto by two spaced electrodes with which it maintains contact as it is advanced at constant speed, the more advanced of said two electrodes consisting of a vessel of molten metal or alloy, and (2) the wire thus heated is quenched at the moment it attains its highest temperature by plunging into the molten metal of said advance electrode, which metal is maintained at a temperature such as will reduce the temperature of the treated wire quickly to a temperature within a desired narrow range.

It is obvious that the speed of wire travel, distance between electrodes, or strength of current may be so modified that the wire will be circuit 28 The of travel and strength of current will be so adjusted that the metal walls of the troughs 3 heated to any desired temperature as it is quenched in the molten metal of the advance electrode. In general, it may be said that it is desirable to so proportion these factors that the wire will attain the desired temperature at the greatest speed consistent with the limitations of steps following in the continuous operation. In practice, this heating will be at a speed such that the wire will have no decarburized surface spots even when unprotected by special atmospheres.

It is our belief that the superior qualities of steel wire heat-treated by our method, whether for drawing, use in springs, or other purpose is to be attributed in large measure to said described initial steps. In particular, wire heated by our method is much more satisfactory in respect to grain structure than that which results from conventional heating, since the uniform heating from the inside and the limited exposure to high temperature results in a product showing little evidence of grain growth.

The oil left on the wires by the wiper 9'will present a surface to which the metal of the molten alloy bath will not adhere. Also the oil 36 on the molten metal of the quench pot 2| will form a thin coat of burnt oil on the hot wires as they enter, which will prevent molten metal from adhering to the wires as they are advanced through the pot. The method of using such oil coatings is the subject matter of our co-pending application No. 320,774, filed February 26, 1940.

Heat treatment of spring steel In heat treating steel wires by our method, and using our disclosed apparatus, to secure the qualities desired in springs, we advance the wires I through the molten alloy contained in contact troughs I (land to and through the molten alloy in the quench pot 2 I, while maintaining a desired difference of electrical potential between the alloy of said troughs and the alloy of said pot by means of a suitable source 21 of E. M. F. in the factors of length of span, speed wires will enter the molten alloy in the quench pot at a temperature at which the iron content of the steel will be in the form of gamma iron dissolving all the carbon. In practice, this temperature will be kept slightly above thecritical temperature or in the case of commercial steels of ordinary analysis the wires will be quenched when at a temperature of approximately 1475" F.

The insulation of the sinker arms l2 from the III will prevent arcing which otherwise would result from currents travelling through the metal walls and through the sinker arms to the rollers 3 which for permanence are made of hard metallic alloy. Likewise the condensers 30 in the circuits 29 connecting the studs l9, which make electrical connection with the troughs l0, and the connector 26, 26, which makes electrical contact with the quench pot 2|, provide paths for the escape of high potentials which in the pot or the troughs would otherwise are from the surface of the metal alloy to the surface of the wire, pitting same.

In the quench pot 2| the alloy is maintained at such a temperature that the wire temperature is dropped in a second or two to a range below those temperatures at which the carbon on transformation will assume pearlite forms, but the temperature of the wire is held by said alloy bath at a temperature above that of rapid done by drawing the wire from the alloy throughan overlying body of quenching oil, which oil will be heated by the alloy beneath it. The wires are drawn from said quench pot and through said oil, keeping them at all times beneath the surface of such oil, into a body of quenching oil in the quench pan 40. When the temperature of the wires has been reduced to substantially atmospheric temperatures the wire is withdrawn from the pan and heated in a conventional lead pot for tempering.

The secondary quench in oil has been found to be very critical, but by our method it may be easily controlled and maintained under constant conditions. The conditions required to give to 1 a particular steel certain definite qualities having been established, the operation can be set for those conditions and continued indefinitely with little or no attention.

As an example, we have heat treated by our method using the described apparatus, Swedish steel wire of No. 10 gauge (.1275 in.) having the following analysis: 0.50, si-0.l6-0-.2l, S-0.020 maximum, P-0.025 maximum. This wire was heated as described to about 1475 F. which temperature we maintained by modifications of the strength of the heating current, made automatically by a photo-electric cell unit responsive to the image of the heated wire, as is well understood in the art. tained at substantially-425 F. and the travelling wires were kept therewithin about 4 seconds. From this alloy they were drawn through quench oil as hereinabove described, which quench oil had a flash point of 455 F. and'a fire point of 510 F. This oil in the portion overlying the alloy thereof. At the end of twenty (20) secondsthe wires were drawn from the oil quench at a temperature of about 125 F. and were passed through a temper pot 53 of lead maintained at approximately 900 F. in which they were retained for about 18 seconds for tempering.

Such wire so treated developed the following physical characteristics? Elastic limit (Johnsons) 214,000 lbs.; yield point (2% method), 222,000 lbs.; tensile strength (p. s. 1.) 234,000 lbs.; percentum elongation in 2 inches, 9; percentum reduction in area 60; hardness, Rockwell C, 45-47. 4 7

As another example commercial steel wire of No. 13 gauge (diameter 0.091 inch) was heat treated by conventional methods and by our method and the results compared. This steel had the following, analysis: C0.63, Mn-1.01, Si--0.l9, P--0.017, and 8-0.022. A bundle was divided and part No. 1 was heated conventionally in a furnace 'to a temperature of 1500 F., quenched in oil and temper drawn in a lead bath at 800 F. Part No. 2, heat treated by our method and apparatus, was heated to 1475 F. as it entered the alloy quench pot which was maintained at approximately 425 F. In three seconds it was drawn from the alloy quench at a temperwhich it was temper drawn in a lead pot at 800 F. The physical properties of the two parts so treated checked as follows:

No 1 No. 2

Tensile strength (lba) p.s.i 248, 000 248, 000 Elastic limit (Johnson's) p.s.l 203, 000 229, 000 Elongation Eperceut in 10 in.) 3. 4 3. l Elongation percent in 2 in. 6.3 5.2 Reduction in area (percent). 53. 64. 8 Torsion (No. twists in in.). 16. 0 26. 0 Hardness (Rockwell C) 47. 0 48.0

Heat treatment of wire ,for drawing qualities Using our method of heat treating we have given wire of Swedish steel of the analysis and gauge of the specimen first abovereferred to, a

novel heat treatment which produced in said wire the characteristics desired for reduction by drawing.

In said novel treatment we heated the advancing wires between the contact troughs l0 and the quench pot 2| as hereinabove described until it attained a temperature of approximately 1475 F. as it entered the molten alloy, of the quench pot which was maintained at a temperature of 500 F. When the temperature of the wires was reduced to the temperature of the quenching alloy they were withdrawn from the said alloy and advanced direct to the lead pot 53 which was maintained at a temperature of 850 F. Be-

tween the quench pot 2| and the lead pct 53 we The alloy of the quench bath was mainre-heated the wires to a temperature of 850 F.

as they entered the lead pct 53 by passing a suitable heating current through said wires which current was supplied thereto through the medium of the molten metals insaid pots 2| and 53. The wires were kept within the molten metal of the pot 53 about 18 seconds after which they were withdrawn and air cooled to atmospheric temperature.

Said wires after being heated as described showed a structure in which very fine constituents were homogeneously arranged, and developed the following physical qualities which will be recognized as excellent for reduction by drawing: tensile strength (p. s. 1.) 170,000 lbs.; percentum of elongation in 2 inches, 11; percentum reduction in area 70; and Rockwell C 34-36.

It will be noted, that in using our apparatus for thus heat treating, the wires are not quenched in the oil bath 40, but are by-passed and rethe molten metals of the quenchpot 2| and the lead pct 53.

Ournovel method of heat treating and described apparatus may be used instead of the process known-as patenting, which is the conventional treatment given steel wire to prepare it for reduction by drawing. ,This patenting is secured by heating the wires as already explained until above the critical temperature for the particular steel. The molten metal of the quench pot is maintained at about 950 F. and the wires after quenching are maintained at said temperature of 950 ,F. for a substantial period before air cooling.- 1

Using our described apparatus as taught in our co-pending application No. 252,954 filed Jan. 26,

1939 we have heat treated half of a bundle of commercial steel wire by heating to 1650 F. by

electrical resistance as the wire advanced from ature of approximately 425 F. and was further the contact troughs III to the lead pct 53. The

molten metal in said lead pot was maintained, at

a temperature of 975 F. and the wire was kept therewithin until quenched to said temperature. From the contact troughs ID the wire was advanced directly into the lead pot 53, through passages insulated for the conservation of heat. The wire was retained within the lead pot 53 which was maintained at 975 F. for about 18 sec- 'was drawn down fro-m 0.0915" to 0.0175 using the following practice: 0.0915" diameter in 6 drafts to 0.0315" diameter. The wire was then copper coated and drawn in 7 drafts through continuous machines to 0.0175 diameter. The physical properties of this wire after thus drawing were as follows: 1st endtensile strength p. s. i. 354,000 lbs. and torsions in 8 inches 101- 108; last end-tensile strength p. s. i. 350,000 lbs., and torsions in 8 inches 105-106.

Another half of the same bundle of wire was patented by conventional methods. In contrast with the similar wire which had been treated by our method, the physical properties of this wire were as follows: elastic limit 68,400 lbs.; yield point 89,100 lbs.; tensile strengthp. s. 1. 146,500 lbs.; percentum elongation 9; percentum reduction 29.2; and Rockwell C 31-34.

Other means and modes of applying the principle of our invention may be employed instead of those explained, change being made as regards the method and means herein disclosed, provided the step or steps stated by any of the following method claims or the equivalent thereof be employed, or provided that the means of any of the following apparatus claims or their equivalents be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. In a method of heat treating steel, in the form of wire and the like, the steps of advancing such material longitudinally at a uniform speed into and through a contact pot containing an electrically conductive liquid and into and through a, quenching bath of molten metal in spaced relation therewith; controlling the temperature of the quenching bath within a desired range; maintaining the material in such quench bath until it attains the temperature thereof; and passing through the section of advancing material, defined between the surface of such quench bath and the surface of the liquid in such contact pot, a current of electricity such as will heat the advancing material progressively to a desired maximum temperature as it enters such quenching bath, such current being supplied thereto through the medium of the molten metal of such quench bath and through th liquid of such contact pot.

2. In a method of heat treating steel, in the form of wire and the like, the steps of advancing such material longitudinally at a uniform speed into and through a contact pot containing molten metal and into and through a quenching bath of molten metal in spaced relation therewith; controlling the temperature of the quenching bath within a desired range; maintaining the material in such quench bath until it attains drawn from said bath of molten metal will be the temperature thereof; and passing through the section of advancin material, defined between the surface of such quench bath and the surface of themolten metal in such contact pot, a current of electricity such as will heat the advancing material progressively to a desired maximum temperature as it enters such quenching bath, such current being supplied thereto through the medium of the molten metal of such quench bath and through the molten metal of such contact pot.

3. In a method of heat treating steel, in the form of wire and the like, wherein an advancing wire is heated to austenitic condition by its resistance to the passage of an electric current and quenched in a bath of molten metal to a temperature below that of pearlite formation and above that of rapid martensite formation, the step of drawing the wire from the molten metal quench directly into an oil bath, through a portion of such oil bath in overlaying relation with a portion of such metal bath, whereby a secondary quench at a slower rate is secured.

4.. A method of heat treating steel, in the form of wire and the like,'comprising the steps of advancing the material longitudinally at uniform speed into and through a quenching bath of molten metal; controllin the temperature of the quenching bath to a. temperature below the range of temperature at which pearlite will form rapidly in the steel when colling from an austenitic condition and above the temperature at which there will be rapid formation of martensite, which temperature of quenching bath when treating commercial steels of the usual analysis will be in the neighborhood of 425 F.; maintaining the material in such quench bath until it attains the temperature thereof; concurrently passing through the advancing material, defined between such quenching bath and a contacting electrode in spaced relation therewith, such a current of electricity as'will heat th material pr,o gressively to a maximum temperature, as it enters such bath, which is in excess of the critical temperature of the steel, whereby it becomes substantially wholly austenitic; and further quenching by drawing from such bath of molten metal directly into and through an oil bath a portion of which overflows such bath of molten metal, whereby a secondary quench is secured wholly within such oil bath, without exposure to atmosphere.

5. Apparatus for the continuous heat treatment of wire and the like advanced therethrough, comprising a quench pot of molten metal; means operative to maintain the molten metal in said quench pot within a desired range of temperature; a contact pot of molten metal in spaced relation with said quench pot; means operative to apply a film of oil to the surface of such wire before it enters said contact pot; means operative to maintain a desired electrical potential between the metal in said pots; and means in each of said pots operative to hold a wire beneath the surface of the molten metal while such wire is drawn successively through said pots.

6. In apparatus as described, in combination, a quench bath of molten metal, and a quench bath of oil, said oil bath overlaying, and being supported by, a section of the surface of said molten metal bath, whereby a wire under treatment,

further quenched in said oil bath before contacting atmosphere. 1

7. In apparatus as described, in combination,

a quench bath-of molten metal, a quench bath of oil, and means operative to flow the oil from said oil bath onto said molten metal, whereby a wire drawn from saidwmolten metal is kept within 011 until it enters the'said oil bath.

8. Apparatus for the continuous heat treatment of wire and the like advanced therethrough, comprising a, contact pot of molten metal; a quench pot of molten metal; sinkers in each pot operative to hold below the surface of the-molten metal, and guide, a wire drawn therethrough for treatment; a source of electro-motiveforce electrically connected in series in a circuit between the molten metal of said pots; an electrical condenser electrically connected in series in a second circuit between the molten metal of said pots; means adapted to maintain the molten metal in said quench pot at a desired temperature, whereby 'a treated wire is partially quenched; a bath of quenchingoil; and means operative to maintain said bath of quenching oil with a substantial portion of the oil overfiowed onto the molten metal of said quench pot, whereby wire under treatment drawn from the said molten metal directly into and through said oil, is further quenched in said oil beforecontacting the atmosphere.

9. Apparatus for the continuous heat treatmerit of wire and the like advanced therethrough,

' comprising a. quench pot of molten metal; means operative to maintain the molten metal .of said pot within a desired range of temperature; means operative to heat by its electrical resistance a wire, advanced at a uniform speed. into, andthrough, said quench pot, to a desired maximum temperature which is attained as it enters the molten metal of said pot; means adapted to maintain such wire beneath the molten metal a of said pot until it has attained substantially the 

